1. Technical Field
The present disclosure relates generally to Coriolis mass flow meters, and more specifically to integrated Coriolis mass flow meters in which flow sensitive member(s) and support structure are integrated, and also to methods of manufacturing such Coriolis mass flow meters.
2. Background Information
Coriolis mass flow meters (also referred herein as “flow meters”) measure a mass flow rate of a fluid flowing through a tube based on Coriolis principles. Typical configurations employ one or two tubes through which the fluid flows and which are oscillated in a controlled manner. Coriolis induced deflections or the effects of such deflections on the tube(s) are measured to calculate the fluid mass flow rate of the fluid flowing through the sensor. Additionally, fluid density can also be measured (independently of mass flow rate) by measuring the change in the sensor's resonant frequency versus fluid density.
Some traditional flow meters use metal alloy flow tubes as the flow sensitive elements. Some traditional methods attach Perfluoroalkoxy alkanes (PFAs) tubular flow sensitive elements to metal supports using an adhesive. However, continuous vibration of the flow sensitive elements causes the adhesive joints to degrade overtime thereby deteriorating the integrity of these traditional flow meters. Additionally, different discrete components of these flow meters are usually made of different materials having different thermal expansion properties. The coupling between the flow sensitive elements and support loses its integrity which results in uncontrolled vibrations and comprises the performance of these devices.
Some traditional methods of manufacturing flow meters that employ etching require submersing and gently agitating tubes in a heated bath containing glycol-diether. While adding costs and complexity to the fabrication of devices, this etching process may not necessarily yield tubes that are suitable for flow meter fabrication on a consistent basis.
Some traditional methods fabricate flow meters via injection molding and form the flow path from a core mold. The core mold is typically made from a low-melting point fusible metal alloy containing a mixture of bismuth, lead, tin, cadmium, and indium with a melting point of about 117 degrees Fahrenheit. When fabricating the flow sensitive members, hot plastic is injected into a mold at temperatures that can exceed 350 degrees Fahrenheit at pressures exceeding 5000 psi. This may impair the comparatively narrow and flexible fusible metal core. As a result, the flow sensitive members are likely to be deformed thereby rendering the device itself unusable. Moreover, metal atoms are likely to mix with and to become embedded within the injected plastic thereby permanently contaminating the flow sensitive members. This can render the device unsuitable for applications that require high-purity processes, such as semiconductor, pharmaceutical or bio-pharmaceutical applications. Moreover, different components of the flow meters fabricated by the traditional injection molding process must all have a similar thickness which is likely to cause structural and/or dynamic design limitations or compromises that could adversely affect and/or limit the performance of the flow meters.
Some traditional fabrication processes employ secondary operations to manufacture the fluid passageways. For example, some processes drill fluid passageways through an entire structure machined from a single piece of polymeric material. Alternatively, some methods form the flow passageways by a combination of a solid core employed within a mold and/or secondary drilling operations after the part is removed from its mold. External holes from coring or drilling are filled by welding or other suitable procedures. Forming the flow passageways with solid cores within a mold and/or drilling may necessarily require the fluid passageways to have larger wall thickness, which can limit these devices' flexibility and measurement sensitivity at low flow rates.
Further traditional methods weld flow sensitive elements onto supports to manufacture flow meters. The flow sensitive elements and supports are typically fabricated from the same polymeric material. However, these supports typically include considerable polymeric material and increase costs of the materials used. Also, application limitations require several internal diameters to change which may cause slurry solids and/or entrained gas/bubbles to accumulate. Further, variations in tube-to-support welding process can introduce dimensional differences and stiffness variations of the flow sensitive element(s) extending from a support, causing the two halves of the flow meter not to vibrate as designed. Last, the welding joint can adversely affect the boundary conditions of the flow sensitive element(s).